1. Field of the Invention
The present invention relates to a method of handling frequency-domain interpolation and a frequency-domain interpolator, and more particularly, to a frequency-domain interpolation method and a frequency-domain interpolator capable of trading complexity and performance and being applied to various pilot intervals.
2. Description of the Prior Art
Orthogonal frequency-division multiplexing (OFDM) is widely adopted in modern communication systems due to its high spectrum efficiency and resistance to multipath fading, for transmitting and receiving signals to increase throughput of the communication systems. Examples of the communication systems are wireline communication systems such as asymmetric digital subscriber line (ADSL) and power line communication (PLC), and wireless communication systems such as wireless local area network (WLAN), Digital Video Broadcasting (DVB) and Long Term Evolution-advanced (LTE-A).
In general, when a communication system employing the OFDM operates, a part of the subcarriers is used for channel estimation by a transmitter of the communication system, wherein the subcarriers are available subcarriers used by the transmitter and a receiver of the communication system. Thus, the receiver can obtain channels (e.g., channel frequency response (CFR)) corresponding to all the subcarriers via the part of subcarriers. As a result, data transmitted via the subcarriers can be recovered by using the estimated channels. In detail, the transmitter arranges pilots known by both the transmitter and the receiver on the part of the subcarriers (i.e., pilot subcarriers). For example, the pilots can be arranged equally spaced on the subcarriers, and the data are arranged on the rest of the subcarriers (i.e., data subcarriers). Thus, when the transmitter transmits an OFDM signal (i.e., on the time-domain) composed of the subcarriers, the pilots and the data are both transmitted to the receiver. After receiving the OFDM signal, the receiver not only can use the pilots for estimating the channels corresponding to the pilot subcarriers, but can also for estimating the channels corresponding to the data subcarriers. Thus, after estimating the channels corresponding to the data subcarriers, the receiver can perform signal processing techniques such as equalization, demodulation, etc., by using the estimated channels, to recover the data on the data subcarriers.
However, when performing the channel estimation, especially performing frequency-domain interpolation in the channel estimation, it is hard to trade between hardware cost and edge performance, wherein the edge performance is performance of edge of the subcarriers. The edge of the subcarriers is easily affected by interference. For example, an order of the frequency-domain interpolation should be increased, to reduce inband interference and outband interference. But, the hardware cost is increased and the edge performance is decreased due to the increased order. Oppositely, the order of the frequency-domain interpolation can be decreased to reduce the hardware cost and increase the edge performance. But, the inband interference and the outband interference are increased due to the decreased order. Thus, it is hard for the receiver to trade between the inband interference, the inband interference, the hardware cost and the edge performance. On the other hand, the transmitter can adjust a pilot interval (i.e., density of the pilots) which is a distance between neighboring pilots, according to causes such as a channel profile, an amount of overhead, and etc. For example, although the pilot interval is 3 in the DVB-Terrestrial (DVB-T) system, i.e., there are three data between every two neighboring pilots, the pilot interval can be 3, 6, 12 or 24 in the new DVB-T system, i.e., the DVB-T2 system. Correspondingly, the receiver needs to process the OFDM signal transmitted with various pilot intervals. Thus, realizing the frequency-domain interpolation with a low complexity in the receiver in the DVB-T2 system is an important problem to be solved.